A silicon die on which a semiconductor device is implemented will generate heat during operation of the semiconductor device. Generally, if the heat is allowed to accumulate beyond a critical point, the semiconductor device may cease to operate properly. Consequently, previous techniques for packaging silicon dies have incorporated a device known as a "heat spreader," so named because it served to dissipate heat from a silicon die. Prior heat spreaders were formed as a solid metal sheet, to which a silicon die would be attached over the die's entire bottom surface. These prior heat spreaders, however, suffered from numerous problems.
For example, mold compound, which is used to encase a silicon die in a packaged semiconductor device, does not adhere to metal as well as it adheres to silicon. Adhesion between materials in a packaged device is desirable because such adhesion enhances the integrity of the package. That is, the packaged device is better able to withstand various forces that may act upon it, such as pressure created by the vaporization of internal moisture during a baking treatment. With prior heat spreaders, mold compound could only contact a silicon die on an upper surface. Contact between mold compound and the silicon die at the die's bottom surface was prevented by the solid sheet of the heat spreader. Consequently, prior heat spreaders weakened the integrity of a packaged device.
Furthermore, packaged semiconductor devices which incorporated prior heat spreaders were especially moisture sensitive. This moisture sensitivity was largely attributable to the fact that the materials from which the silicon die and the heat spreader were formed did not expand and contract at the same volume rate in response to the addition or substraction of heat. The silicon die was formed from silicon, whereas the prior heat spreader was typically formed from metal. Metal expands and contracts more rapidly than silicon when exposed to changes in heat. Thus, during a bake process intended to remove moisture from a packaged semiconductor device, mechanical stress was generated over the area at which the silicon die and the heat spreader were attached--i.e., the entire bottom surface of the silicon die. If the packaged semiconductor device was baked for a long time in order to remove a large amount of moisture, the mechanical stress between the silicon die and the heat spreader would cause the semiconductor packaging to burst in a "popcorn effect."